The present invention relates in general to belt-drive continuously variable transmissions, and particularly to a belt-drive continuously variable transmission of the kind wherein a belt includes an endless carrier and a plurality of transverse elements positioned transversely on the endless carrier, the transverse elements being arranged in such a manner that adjacent two of the transverse elements are held in contact with each other, each transverse element having a rocking edge and rotatable about the rocking edge in the longitudinal direction of the belt for thereby enabling the belt to be wound around a drive pulley and a driven pulley.
A belt-drive continuously variable transmission is known from U.S. Pat. No. 5,439,422.
A problem of a prior art belt-drive continuously variable transmission is that each transverse element of a drive belt cannot be brought into contact at the entire side face thereof with the contact surface of a pulley but only partially, thus causing partial and excessive wear of the transverse elements and lowering of the coefficient of friction between the transverse element and the pulley. Thus, it is considered that the prior art belt-drive continuously variable transmission admits of improvement in the torque transmission capacity of the drive belt.
More specifically, in a continuously variable belt-drive transmission shown in FIGS. 9 to 12, each transverse element 2 of a drive belt 1 is tiltable or rotatable relative to adjacent element 2 about a rocking edge 6 for enabling the drive belt l to be wound around a drive pulley 4 and a driven pulley 5. Each transverse element 2 has a pair of converging side faces 2f for contact with the respective contact surfaces 4f(5f) of conical discs 4a(5a) and 4b(5b) of each pulley 4(5). The side faces 2f and 2f of each transverse element 2 are adapted to contact, at the entirety thereof, the respective contact surfaces 4f(5f) and 4f(5f) of the fixed conical disc 4a(5a) and the movable conical disc 4b(5b) substantially uniformly. Thus, a thrust N exerted by the pulley 4(5) against the transverse element 2 is distributed uniformly as shown in FIG. 11. Accordingly, the center C of action of the thrust N against the transverse element 2, when observed in FIG. 11, is positioned nearly at the center of the width of the side face 2f. 
FIG. 12 shows a portion of a row of the transverse elements 2. Now, it is assumed such a condition wherein a torque of the pulley 4(5) is transmitted to the transverse element 2-1 to allow the transverse element 2-1 to be pressed against the adjacent transverse element 2xe2x80x942. This condition can be substituted for such a condition wherein a driving force F directed along the contact surface 4f(5f) of the pulley 4(5) acts upon the center C of action of the thrust N against the transverse element 2. In this instance, since there is a distance xcex94L between the center C of action of the thrust N and the rocking edge 6 when the transverse element 2 is observed in a side elevation shown in FIG. 12, a moment M (M=Fxc3x97xcex94L) acts upon the transverse element 2 in the direction indicated by the arrowhead.
Thus, the transverse elements 2, when operated to transmit a driving force F, are caused to tilt or rotate backward (i.e., in the direction opposite to the direction of advance of the drive belt 1) by the moment M while passing around the pulleys 4 and 5. Due to this, the side faces 2f and 2f of each transverse element 2 are not brought into contact at the entirety but only partially, i.e., only at the hatched area X of each side face 2f as shown in FIG. 12, thus causing the above described problem of partial and excessive wear of the transverse elements and lowering of the coefficient of friction between the transverse element and the pulley.
It is accordingly an object of the present invention to provide a novel and improved belt-drive continuously variable transmission which can attain an improved torque transmission capacity by preventing backward tilting or rotation of the transverse elements and thereby partial and excessive wear of the side faces of each transverse element, being causative of lowering of the coefficient of friction between the drive belt and the pulley.
To accomplish the above object, there is provided according to the present invention a novel and improved belt-drive continuously variable transmission which comprises a drive pulley and a driven pulley, and a belt engaged with the drive pulley and the driven pulley and including an endless carrier and a plurality of transverse elements closely arranged on the carrier. Each of the transverse element has an edge and rotatable about the edge in the longitudinal direction of the belt for enabling the belt to be wound around the drive pulley and the driven pulley. Each of the transverse elements has converging side faces for contact with contact surfaces of the drive pulley and the driven pulley. Each of the side faces, when observed in a plan view of each of the transverse elements, is protruded and curved toward each of the contact surfaces, only at a portion adjacent the edge.